Stabilised compositions having antibacterial activity

ABSTRACT

A stabilised composition having antibacterial, antiviral and/or antifungal activity, said composition comprising silver ions and a ligand, characterised in that the composition comprises a complex of silver and a ligand selected from the group consisting of 5,5-disubstituted hydantoins in which the substituents do not comprise conjugated unsaturated bonds and barbituric acid and derivatives thereof stabilising silver ions against reduction to free silver in a hydrophilic environment, and that the composition has a solubility in water higher than 10 mg Ag/l is stable during sterilisation and retains the activity without giving rise to darkening or discoloration of the dressing during storage.

This is a nationalization of PCT/DK01/00616 filed Sep. 26, 2001 andpublished in English.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to stabilised compositions havingantibacterial, anti-viral and/or antifungal activity, to a method ofproducing such compositions, medical devices having a coating comprisingsuch compositions, and the use of the stabilised compositions forproducing a wound dressing, an ostomy appliance, an incontinence device,other medical devices or hydrophilic coatings.

The antiseptic activity of silver compounds is a well known propertywhich has been utilised for many years. The bacteriostatic andfungistatic effect is caused by the silver ion and a simple compoundwhich has been used clinically is for instance silver nitrate. Silvernitrate in concentrations of 0.5-1% in water shows disinfectantproperties and is used for preventing infections in burns or forprophylaxis of neonatal conjunctivitis. For another silver compound,silver sulfadiazine, the antibacterial effect of the sulfadiazinemolecule is further enhanced by the complexing with the disinfectingsilver ion. In contrast to the silver nitrate, the solubility of thesilver sulfadiazine complex is low and hence, both of the two activeparts are only present in solution in low concentrations but may bepresent over a longer period of time before being washed out at site tobe treated. The silver sulfadiazine is intensively used in the treatmentof wounds, in particular burns, under the trademarks Silvadene® andFlamazine®. Silver-protein-combinations are yet other antisepticformulations which have been used in low concentrations as eye drops.

2. Description of the Related Art

Bacteriostatics based on the silver ion are further used in variousmedical devices. One example of such application is the use in the wounddressing sold by Johnson & Johnson under the trademark Actisorb® whichis an activated charcoal cloth dressing. Another example is the wounddressing sold under the trademark EZ-Derm by Genetic Laboratories whichdressing is a modified pigskin impregnated with a soluble silvercompound intended for treatment of burns. A number of patents disclosescompositions or devices showing antiseptic properties based on contentsof silver compounds. EP 272 149 B1 discloses a medical dressing of the‘hydrocolloid’ type containing and releasing active components. Silverchloride is a specific antiseptically acting compound mentioned in thispatent.

A specific advantage in using the silver ion as bacteriostatic agent isthe general lack of formation of bacterial tolerance to the compound.This is in contrast to many types of antibiotics. However a majordrawback when using ionic silver for bacteriostatic purposes is thereduction of the ion to free silver which results in dark staining. Suchstaining has been reported to give potentially permanent pigmentation ofthe skin, the so-called argyria. It is commonly recognised that silvercontaining compounds will discolour by influence of light and or heat,and it will often be found that sterilisation by radiation may lead to aunsatisfactory change of the colour of a composition in which it iscomprised, irrespective of the use in a solution, cream or gel or amedical device. Furthermore, such antibacterial compositions are oftenintended used in connection with medical or cosmetic products undercircumstances where a discoloration is very unfortunate and potentiallyprecluding for the use.

Recently, principles of antimicrobial metal-based compositions beingphoto stable, have been disclosed in U.S. Pat. No. 5,326,567 to Capelliand in U.S. Pat. No. 5,429,819 to Oka. In U.S. Pat. No. 5,326,567 a‘host-guest’ relationship between silver ions and acyclic polyethers isaccomplished through the use of excess of halide ions. In U.S. Pat. No.5,429,819 is disclosed a photo-stable composition comprising a complexof the silver ion with a thiosulphate salt carried on a porousparticulate carrier. In U.S. Pat. No. 3,911,115 (DE patent No. 22 60536) a cycloheptaamylose (β-cyclodextrin) alkanol amine compound isclaimed to posses stabilising effect on silver. However, in praxis thecycloheptaamylose alkanol amine complex is not effective in preventingdiscolouring. In U.S. Pat. No. 5,298,624 Lasker claims stableorganometallic complexes of 5,5-diphenyl-2,4-imidazolidenedione(diphenylhydantoin) used as biocides. One such material is thesilver-diphenyl hydantoin complex, which, however, it is poorly solublein water. In U.S. Pat. No. 2,336,131 Schaffer disclose the formulationof silver allantoinate for antibacterial use. The compound is intendedfor medical use. However the compound does not show high stabilityagainst light. In U.S. Pat. No. 3,930,000 Margraf discloses silver-zincallantoinate for topical use for control of bacteria and fungi. Thesecompound, however, show a low solubility. In International PublishedPatent Application No. WO 00/09173 Pedersen et al teaches thestabilisation of silver by complexing with amines presenting a lone pairof electrons.

It is commonly recognised that compounds containing silver willdiscolourise in presence of light and/or heat, as well as it often willbe found that radiation sterlisation process will lead to adissatisfactory change of colour of the composition in which it iscomprised whether it is in a cream or a gel or a medical device.Moreover, such antibacterial compositions are often intended for use formedical or cosmetic purposes under which circumstances a discolorationis very unfortunate and potentially prevents the use of silver ions forsaid use.

It is an object of the present invention to provide complex structurerendering silver ions stable against loss of the antiseptic activity andagainst darkening due to reduction of the silver ions or the formationof darkly stained sparingly or insoluble silver compounds. Furthermore,it is an object to provide a complex structure rendering silver ionsavailable sufficiently quickly and in a sufficiently high and lastingconcentration to ensure that an effective antiseptic activity isobtained. Still further it is an object to provide a method forpreparing such complexes without losing the antiseptic activity of thesilver ions. Further it is the objective to incorporate such intoentities in combination with hydrophilic polymers, e.g. in hydrocolloidparticles or coatings enabling a sufficient release of silver for theestablishment of a bactericidal burst.

Such entities may be medical devices or instruments like catheters,guide-wires, wound dressings or similar.

The use of the silver complex of diphenyl hydantoin as taught by Laskerhas the advantage of easy processing and for certain applications slowrelease. However, it is a major drawback that the compound has lowsolubility and lacks sufficient stability against irradiation and light.The silver allantionate likewise show low stability against light andhas limited solubility. Especially when the compound is used incombination with hydrophilic polymers often used in the context ofmedical devices it may be impossible to obtain a high release of silverdue to low solubility of the compound in biological environments andsimilarly impossible to incorporate such in the device.

It has surprisingly be found that certain silver complexes comprisingsilver and a ligand selected from the group consisting of5,5-disubstituted hydantoins in which the substituents do not compriseconjugated unsaturated bonds and barbituric acid and derivatives thereofpossess very good stability.

SUMMARY OF THE INVENTION

The present invention relates to stabilised compositions havingantibacterial, antiviral and/or antifungal activity.

Furthermore, the invention relates to a method of producing compositionshaving antibacterial, antiviral and/or antifungal activity.

Still further, the invention relates to medical devices being coatedwith, impregnated with or blended during production with stabilisedcompositions having antibacterial, antiviral and/or antifungal activity.

The invention also relates to a method of treating or preventinginfection in a human being by applying a medical device such as a wounddressing or an ostomy appliance, an incontinence device, or other devicesuch as a catheter comprising a hydrophilic coating which medical devicecomprises a stabilised composition having antibacterial, antiviraland/or antifungal activity.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention relates in its broadest aspect to a stabilisedcomposition having antibacterial, antiviral and/or antifungal activitywhich composition is characterised in that it comprises complexes ofsilver ions and a ligand selected from the group consisting of5,5-disubstituted hydantoins in which the substituents do not compriseconjugated unsaturated bonds and barbituric acid and derivatives thereofwhich complexes have a solubility in water higher than 15 mg Ag/l havebeen found to stabilise the silver ions against darkening by UV light.

Suitable compounds are 5,5-disubstituted hydantoins in which thesubstituents do not comprise conjugated unsaturated bonds, preferably5,5-dialkylsubstituted hydantoins and barbituric acid and derivativesthereof, preferably dialkylbarbiturates.

In the present context, “alkyl” is intended to designate straight orbranched or cyclic alkyl groups having 1-12 carbon atoms, more preferred1-6 carbon atoms and most preferred 1-4 carbon atoms such as methyl,ethyl, propyl, isopropyl, n-butyl, isobutyl or tert.butyl. “Cycloalkyl”is intended to designate cyclic alkyl groups comprising 3-15 carbonatoms, preferably 4-10 and most preferred 5-7 carbon atoms. The twomoieties may be the same or different.

Hydantoins and barbituric acid derivatives suitable for use in thepresent invention are also such comprising a further substitution of analkenyl, alkynyl, acyl moiety.

“Alkenyl” or “alkynyl” are intended to designate straight or branchedhydrocarbon groups comprising a carbon-carbon double or triple bond andhaving 2-12 carbon atoms, preferably 2-6 carbon atoms and most preferred1-4 carbon atoms. “Acyl” is intended to designate C₂-C₁₀ alkanoyl,alkenoyl or alkynoyl groups, preferably such groups comprising 2-6carbon atoms and most preferred 2-4 carbon atoms or aroyl having 1-4carbon atoms in a side chain. An especially preferred acyl group is theethanoyl group.

Preferred compositions are such wherein the ligand is an aliphatic oralicyclic substituted hydantoin.

Preferred compounds among the above are 5,5-dimethyl-hydantoin,5,5-diethyl-hydantoin, 5,5-dipropyl-hydantoin,1-acetyl-5,5-dimethyl-hydantoin, 5,5-dimethyl-barbituric acid, and1,5,5-trimethyl-barbituric acid. All these complexes shown a solubilityin water above 20 mg Ag/l.

Especially preferred is 5,5-dimethyl hydantoin.

These compositions of the invention have a solubility in water higherthan 10 mg Ag/l, preferably more than 15 mg Ag/l and more preferred morethan 25 mg Ag/l. The solubility is preferably more than 50 mg Ag/I andmost preferred more than 100 mg Ag/l.

In another preferred embodiment of the invention, the compositioncontains a second silver compound with a solubility less than 10 mgAg/l. Such compositions provide a graduated release profile bothoffering high initial release of silver and a prolonged period of silverrelease at a high level.

The composition of the invention typically comprises complexes of silverand compounds of the formula (I) in the ratio 1:1. In a preferredembodiment, the compound of the formula (I) is present in excess i.e. inratios of more than 1:1, preferably 1:2. Such complexes show anincreased solubility in water.

When providing complexes of the above ligands and silver, a secondcation is to be present in order to counterbalance the charge of theligands. Such counter ions are preferably ions of alkaline metals suchas lithium, sodium or potassium, preferably sodium; or ammonium ions.

Furthermore, it has been found that the silver complexes of theinvention are stable against reduction by influence from UV light andirradiation in hydrophilic compositions.

It has been found that ligands especially suitable for the purpose ofthe present invention are 5,5-disubstituted hydantoins and barbituratesin which the substituents do not absorb UV light, i.e. comprisingsubstituents not comprising conjugated unsaturated bonds.

Preferred types of complexes are complexes with hydantoins orbarbiturates. In the group of hydantoins the aliphatic or alicyclicsubstituted hydantoins for instance 5,5-dimethyl hydantoins and5,5-diethyl hydantoins are preferred due to a very high stability.

In the present context, the term “stable” is intended to cover animprovement of the stability of the silver ion against the influence ofUV light which normally leads to formation of dark stained free silver.A preferred stability may be expressed as a distance in CIE-lab ColorSpace below 25, preferably below 10.

Solid silver or solutions of silver salts may fairly easily bestabilised against heat and UV light when stabilised with dextrins andthiosulfates. These types of complexes has, however, shown not to bestable in presence of hydrophilic polymers especially the strongly polaror ionic polymers. The stabilisation of silver according to theinvention also provides stability in the presence of such polymers. Asionic and polar polymers are used increasingly in medical devices and assilver compounds are effective antibacterial agents combinations ofthese are very desirable. The present invention offers the option ofusing such combinations without risking discoloration as well as methodsof producing such and medical devices comprising the same.

The compositions of the invention may be e.g. used in wound dressings.In particular the material is suitable for incorporation in traditionalgauzes and compresses, hydrocolloid dressings or xerogel dressings. Insuch dressings the silver composition according to the invention mayreadily be incorporated by dissolution in water and impregnation intodressings like gauze, or they may be introduced as a component of saiddressing, e.g. a component of an adhesive composition, by a manner knownper se. A method for incorporation in hydrocolloid dressings isdisclosed in EP Patent 591,440, Samuelsen et al. A method forincorporation of the composition in alginate fibre dressings or similardressings is by simply adding the composition to the water basedsolution comprising the alginate before this is further processed into afibrous material. Introduction may also take place in the form of apowder which is easily obtained for instance by grinding a lyophilisedor spray-dried material. In wound dressings the compound may beintroduced into the adhesive for fixing the dressing to the wound siteor into another part of the dressing, for instance a foam pad.

The compositions of the invention and formulations thereof may be usedfor antibacterial, antiviral or antifungal use in the area of human orveterinary medicine. Such formulations may be in the form of a cream orgel intended for dermatological use, in wounds or other body cavities.Formulations may also be in form of powders for similar purposes or forskin folds or athletes foot or the like in the veterinary area.

Not only wound dressings but many other types of products are suitablefor incorporation of the silver compositions of the invention forinstance foamed products or vaginal inserts for use in the continencecare, condoms, male external urine catheters, skin adhesives etc.

Furthermore, the compositions may be used in products not necessarilybeing in direct contact with the body such as powders for removal ofodour in incontinence pads or for incorporation into ostomy pouches.

The silver compositions of the invention may also be used in implantsand sutures or materials that are intended to be left for a period inbody cavities. This will be advantageous in connection with surgerywhere the risk of infection is always latent. Systemic prophylactictreatment with antibiotics in combination with a proper antiseptictreatment of the skin are in most cases common practice. Often medicalarticles that are implanted or for other reasons left in a surgicalopening are carrying antiseptics or even antibiotics. The presentinvention offers an advantageous alternative to known compositionscomprising silver as the compositions of the invention have been foundto have broad antiseptic properties and to be stable during storing andin use. Moreover, the compositions of the invention are very suitablefor controlled release for instance when incorporated in polylactic acidfor sutures or implants or when incorporated in implants based onhydroxyl apatite. Furthermore, the silver compositions of the inventionare suitable for incorporation into haemostatics based on e.g. alginatefibres or foam dressings as well as materials based on collagen orgelatine. Still further, the compositions may be introduced intogel-like materials intended to be protecting covers for e.g. anastomosesformed in bowel or vascular surgery.

The invention also relates to a medical device comprising animpregnation or coating comprising a silver compound in the form of acomplex of silver and a ligand selected from the group consisting of5,5-disubstituted hydantoins in which the substituents do not compriseconjugated unsaturated bonds and barbituric acid and derivativesthereof.

Such complex may advantageously be associated with a coating of one ormore hydrophilic polymers.

Hydrophilic polymers to be used in the compositions according to theinvention are suitably selected from synthetic hydrophilic polymers andderivatives of animal or vegetable hydrophilic polymers. In a preferredembodiment of the invention the hydrophilic polymer is selected from thepolysaccharides. Polysaccharides to be used according to the inventionare preferably cellulose derivatives. Preferred cellulose derivativesare sodium carboxymethylcellulose and hydroxyethylcellulose.

In another embodiment of the invention the hydrophilic polymer isselected from the alginates. An alginate is preferably the sodium and/orcalcium alginate. It has been found to be especially suitable when thealginate has been formed from an alginate comprising an alkali metalsuch as lithium, sodium, or potassium ions, preferably sodium ions; orammonium ions that the alginate is subjected to ion exchange usingcalcium nitrate as this will not give rise to presence of chloride ionswhich would cause a precipitation of silver in the form of sparinglysoluble silver chloride.

In yet another embodiment of the invention the hydrophilic polymer isselected from collagens or fragments thereof. Preferably porcinecollagen is used.

In yet further embodiments of the invention the hydrophilic polymer isselected from glucosaminoglycans and proteoglycans.

In still another, preferred embodiment the composition according to theinvention is a hydrophilic polymer which forms a gel or xerogel.

The polymers to be used in the compositions of the present invention maybe in the form of a polymer forming a network of crosslinked or noncrosslinked hydrophilic polymer.

Preferred hydrophilic polymers are optionally modified polysaccharidesand preferably from the group of cellulosic derivatives having varioussubstituents. These polymers are readily available from the nature orfrom synthetic modification. Other preferred polymers are polylacticacid, hydroxypolyesters, polyvinyl ether, polyvinyl alcohol,polyvinylpyorrolidone, polyacrylates, hydrophilic polyurethanes,polymaleic acid, copolymers of anhydrides and polymers of natural originlike glucosaminoglycans, collagen, gelatine and fibrin or the like aswell as copolymers or derivatives thereof.

Further, such polymers may be crosslinked into a three-dimensionalnetwork.

The concentration of silver in a composition with a hydrophilic polymeraccording to the invention is preferably from 0.05 to 20% by weight ofthe dry matter, more preferred from 0.5 to 5% by weight of the drymatter.

Furthermore, the invention relates to a method of producing compositionshaving antibacterial, antiviral and/or antifungal activity andcomprising a complex of silver and a ligand selected from the groupconsisting of 5,5-disubstituted hydantoins in which the substituents donot comprise conjugated unsaturated bonds and barbituric acid andderivatives thereof in which a silver salt is dissolved in water, a5,5-disubstituted hydantoin in which the substituents do not compriseconjugated unsaturated bonds or barbituric acid or a derivative thereofis dissolved in water and added to the solution of the silver salt at acontrolled pH and the resulting solution is left for a period of from 2to 100 hours, optionally after adjusting the pH using a value of 7-11,the resulting mixture is isolated and optionally dried and micronised.The isolation may be carried out in analogy to the standard isolation ofsimilar compounds.

The composition according to the invention may be utilised withoutintermediary drying and optional micronisation and e.g. added directlyto a hydrophilic polymer.

Still further, the invention relates to a method of treating orpreventing infection in a human being by applying a medical device suchas a wound dressing or an ostomy appliance, an incontinence device, orother device such as a catheter comprising a hydrophilic coating; whichmedical device comprises a stabilised composition having antibacterial,antiviral and/or antifungal activity, said medical device coated with,impregnated with or blended with a complex of silver and a ligandselected from the group consisting of 5,5-disubstituted hydantoins inwhich the substituents do not comprise conjugated unsaturated bonds andbarbituric acid and derivatives thereof.

Yet further, the invention relates to a medical device such as a wounddressing or an ostomy appliance, an incontinence device, or other devicesuch as a catheter comprising a hydrophilic coating; which medicaldevice comprises a stabilised composition having antibacterial,antiviral and/or antifungal activity, said medical device being coatedwith, impregnated with or blended with a complex of silver and a ligandselected from the group consisting of 5,5-disubstituted hydantoins inwhich the substituents do not comprise conjugated unsaturated bonds andbarbituric acid and derivatives thereof.

An incontinence device of the invention may be a urisheath or a catheteror guide wire comprising a hydrophilic coating or adhesive comprising acomposition according to the invention.

An ostomy appliance of the invention may be an ostomy bag or a body sidemember or any ostomy device such as a closure comprising a compositionaccording to the invention.

The invention is explained more in detail in the working examples belowdisclosing embodiments and properties of compositions of the invention.It is evident that many variations may be made without diverging fromthe invention the scope of which is set forth in the appended claims.

Materials and Methods

-   97% 5,5-Dimethyl-hydantoin (Commercially available from Aldrich)-   98% 5,5-Dimethyl barbituric acid (Commercially available from Fluka)-   Sodium hydroxide (Analytical Grade, commercially available from    Merck)-   Purified Water (Demineralised water, conductivity 0.04 micros)-   Polyvinyl pyrrolidone—PVP K90 (Commercially available from    International Speciality Products)-   Hypol 2002 (An isocyanate prepolymer, commercially available from    Hampshire Chemical, Inc.)-   PE 6200, Surfactant (Commercially available from BASF)-   Silver Nitrate powder (63.5% pure silver, commercially available    from Johnson Matthey)    Synthesis of Ligands for Complexing with Silver:    1-Acetyl-5,5-dimethyl-hydantoin:

25.6 g 5,5-dimethyl-hydantoin, 50 g acetic anhydride and 5 drops ofconc. sulphuric acid is refluxed for 1 h, and evaporated to dryness atreduced pressure. 10 ml Ethanol is added, the slurry is first heated,then cooled in an ice bath and filtered. The solid residue wasrecrystallised in 100 ml ethanol and dried. Yield 12.3 g (36%)

5,5-Diethyl-hydantoin:

135 g ammonium carbonate, 58.5 g potassium cyanide, 525 g purified waterand 64.5 g 3-pentanone is heated for 24 h/75° C. in a closed vessel withvigorous stirring. The vessel is cooled in an ice bath, and the reactionmixture is filtered, the crystals rinsed with ice-water and dried. Yield45 g (38%)

5,5-Dipropyl-hydantoin:

27 g ammonium carbonate, 11.7 g potassium cyanide, 105 g purified waterand 17.1 g 4-heptanone is heated for 24 h/75° C. in a closed vessel withvigorous stirring. The vessel is cooled in an ice bath, and the reactionmixture is filtered, the crystals rinsed with ice-water. The crystalsare dissolved in ethanol, 3 g of activated carbon is added, the mixtureis stirred for 1 h and filtered. The product is recrystallised fromethanol/purified water and dried. Yield 24.2 g (88%).

5-Methyl-5-isobutyl-hydantoin:

27 g ammonium carbonate, 11.7 g potassium cyanide, 105 g purified waterand 15.0 g methyl-isobutyl-ketone is heated for 24 h/75° C. in a closedvessel with vigorous stirring. The vessel is cooled in an ice bath, andthe reaction mixture is filtered, the crystals rinsed with ice-water anddried. The crystals are dissolved in 100 ml 1M NaOH, end precipitatedwith slow addition of 20% HNO₃. The mix is filtered and rinsed withpurified water. The solid is suspended in 100 ml purified water, stirredvigorously for 1 h, filtered and dried. Yield 13.8 g (54%)

UV Light Stability Test:

1.5 g of complex was placed in a 50 mm Pyrex petri dish. This wascovered with a 56 mm Pyrex lid with a UV-cut off at approx. 280 nm andplaced 100 mm under a UV lamp (UVASPOT) 400/T 450W metal halide highpressure lamp, Dr. K. Hönle GmbH) for 30 minutes.

The colour was measured, with a Minolta CR300 colour measurementapparatus (CIE-Lab colour coordinates) before (1) and after (2)irradiation. Measurements were made approx. 1 mm above the complex. Thedistance in colour-space was calculated using the formulaDist=√{square root over (ΔL ² +Δa ² +Δb ²)}, where “L”, “a”, and “b” arethe CIE-Lab Colour CoordinatesSolubility for 1:1 Complexes:

Procedure for determination of solubility: 250 mg of the substance to beexamined is placed in a 15 ml PP centrifuge tube and 10 ml purifiedwater is added. The tube is placed on a vortex mixer for 1 h (1500min⁻¹) and the tube is centrifuged (3000 min⁻¹/30 min). The water isdecanted off and discarded, and another 10 ml purified water is added.This is repeated 2 times, and after the third centrifugation, the liquiddecanted off is filtered (0.22 mm PVDF), preserved with nitric acid andthe silver concentration is determined by atomic absorption spectroscopyafter appropriate dilution.

Solubility for 1:X Complexes (Where x Exceeds 1):

0.15 g 1:1 complex was suspended in 10 ml 0.1 M solution of thecorresponding sodium hydantoinate (Ligand being in a molar excess of the1:1 complex), and C_(Ag) is determined with Atomic AbsorptionSpectroscopy (MS) using a Perkin Elmer A-Analyst 100 apparatus afterfiltration and appropriate dilution at ambient temperature. In case thatthis yields in a clear solution the solubility is simply reportedas >5.000 mg Ag/l.

Experimental Part

EXAMPLE 1

Determination of solubility of complexes of silver with various ligands.The solubility was determined as stated above and the results are statedin the below Table 1.

TABLE 1 The solubility was determined as mg Ag/l water: ComplexSolubility Silver Complex Ag:ligand mg Ag/l Ag/hydantoin 1:1 3Ag/hydantoin/Na 1:2 >5.000 Ag/5,5-dimethyl-hydantoin 1:1 104Ag/5,5-dimethyl-hydantoin/Na 1:2 >5.000 Ag/5,5-diethyl-hydantoin 1:1 260Ag/5,5-diethyl-hydantoin/Na 1:2 >5.000 Ag/5,5-dipropyl-hydantoin 1:1 27Ag/5,5-dipropyl-hydantoin/Na 1:2 >5.000Ag/1-acetyl-5,5-dimethyl-hydantoin 1:1 1.100Ag/5-isobutyl-5-methyl-hydantoin 1:1 12 Ag/5,5-diphenyl-hydantoin 1:1 11Ag/5,5-diphenyl-hydantoin/Na 1:2 0.7

EXAMPLE 2 Preparation of Silver Complexes

Silver hydantoinate: 12 g hydantoin and 100 ml 1 M NaOH was dissolved in100 ml purified water. 16.3 g AgNO₃ dissolved in 50 ml purified water isadded slowly with stirring. The suspension is left with stirring for 2 hand filtered. The white solid is resuspended in 200 ml purified water,stirred for 2 h, filtered, washed with acetone and dried. Yield 19.0 g(96%)

Silver 5,5-dimethyl-hydantoinate: 12.3 g 5,5-dimethyl-hydantoin and 4.2g NaOH is dissolved in 150 ml purified water. 16.3 g AgNO₃ dissolved in50 ml purified water is added slowly with stirring. The suspension isleft with stirring for 2 h and filtered. The white solid is resuspendedin 200 ml purified water, stirred for 2 h, filtered, washed with acetoneand dried

Silver 5,5-diethyl-hydantoinate: 1.87 g 5,5-diethyl-hydantoin and 10.0ml 1 M NaOH is dissolved in 20 ml purified water. 1.70 g AgNO₃ dissolvedin 10 ml purified water is added slowly with stirring. The suspension isleft with stirring overnight, filtered, washed with purified water andacetone and dried. Yield 2.54 g (97%)

Silver 5,5-dipropyl-hydantoinate: 2.21 g 5,5-dipropyl-hydantoin and 10.0ml 1 M NaOH was dissolved in 40 ml purified water. 1.70 g AgNO₃dissolved in 10 ml purified water is added slowly with stirring. Thesuspension is left with stirring overnight, filtered, washed withpurified water and acetone, resuspended in 50 ml acetone, filtered anddried. Yield 2.18 g (75%)

Silver 5-methyl-5-isobutyl-hydantoinate: 1.70 g5-methyl-5-isobutyl-hydantoin was dissolved in a surplus of 25% NH₃(aq)and 1.70 g AgNO₃ in 20 ml purified water is added slowly with stirring.The suspension is stirred overnight, and the purified water is removedat reduced pressure. The solid is suspended in purified water, filtered,washed with purified water and acetone and dried. Yield 2.69 g (97%)

Silver 1-acetyl-5,5-dimethyl-hydantoinate: 8.51 g1-acetyl-5,5-dimethyl-hydantoin was dissolved in 55 ml 1M NaOH and 100ml purified water. 8.49 g AgNO₃ in 40 ml purified water is added slowlywith stirring. The suspension is stirred for another 20 min, cooled withice, filtered, washed with cold purified water and dried.

Silver allantoinate: 1.90 g (12 mmol) allantoin was dispersed in 20 mldistilled purified water and 10.0 ml 1 M NaOH is added while stirring atambient temperature. Allanthoin was in a slight excess to prevent strongalkalinity. 1.70 g silver nitrate (10 mmol) in purified water is addedunder vigorous stirring while white precipitate of the silver complex isform. This is filtered, dried and milled.

EXAMPLE 3

Determination of Relative UV Light Stability of Complexes

Silver allantoinate: attempts to make the complex according to U.S. Pat.No. 2,336,131 gave a product that discoloured extremely easily(rendering a UV light-stability test meaningless), so a modifiedprocedure was adopted:

1.897 g allantoin (12 mmol) was suspended in 20 ml purified water, and10.0 ml 1M NaOH (10 mmol) Was added. 1.70 g AgNO₃ (10 mmol) in 10 mlpurified water was added slowly with stirring, and the suspensionfiltered, rinsed with purified water and acetone and dried yielding ahard solid that was white without traces of discoloration. This wascrushed in a mortar and used as was.

The results of the tests for UV stability is stated in the below Tables2 and 3:

TABLE 2 Visual evaluation of complexes after UV-irradiation:Ag-5,5-diphenyl-hydantoin 1:1 Dark brown discolourationAg-5,5-dimethyl-hydantoin 1:1 White/no trace of discolourationAg-5,5-diethyl-hydantoin 1:1 White/no trace of discolourationAg-5-methyl-5-isobutyl-hydantoin 1:1 White/no trace of discolourationAg-allantoin 1:1 Dark brown/heavily discoloured Ag-hydantoin 1:1 Darkbrown/heavily discoloured

TABLE 3 Colour measured with a Minolta CR300 colour measurementapparatus Compound L1 a1 b1 L2 a2 b2 Dist. Ag-5,5-dimethyl- 94.96 0.29−0.12 96.84 0.31− 0.39 1.90 hydantoin 1:1 Ag-5,5-diethyl- 96.76 0.04−0.67 94.05 0.35− 2.03 3.05 hydantoin 1:1 Ag-5-methyl-5- 92.4 0.03 0.4292.65 0.16− 1.74 1.36 isobutyl-hydantoin 1:1 Ag-hydantoin 1:1 96.67 0.062.62 26.03 10.75 12.84 72.17 Ag-5,5-diphenyl- 93.05 0.71− 2.59 38.7121.06 33.81 66.34 hydantoin 1:1 Ag-allantoin 1:1 92.98 0.53− 2.3 32.714.71 28.41 67.44

Compounds according to the production in example 4 were assessed forstability against UV-light (wave length >280 nm). Milled powders werespread in a 1 mm thick layer in ordinary petri dishes and illuminated bythe UV-light for 30 minutes.

The results show that the compounds of the invention show a clearlybetter stability against discolourisation than known compounds, i.e.having a distance in CIE-lab colour space of <25.

EXAMPLE 4

Preparation of Stabilised Silver Solution (SSS)

In one litre of purified water 79.2 grams (0.6 moles) of 5,5-dimethylhydantoin, 17.2 grams (0.43 moles) of sodium hydroxide and 34 grams (0.2moles) of silver nitrate was dissolved (the silver nitrate and the 5,5Di Methyl Hydantoine were dissolved separately and mixed when the twosolutions were clear to avoid precipitation). This solution wasdesignated Stabilised Silver Solution (SSS). The Silver concentration inthe SSS was app. 2% w/w.

The SSS is simple to incorporate in both wet and dry wound careproducts, due to the stability of the SSS for obtaining antibacterialwound care dressings.

In the below four examples is demonstrated how the SSS can beincorporated into foams, amorphous hydrogels and hydrogel sheets. It issimple to use other formulations for preparing products in all the 3product categories mentioned above. The SSS can be included in almostany other product category like films, alginates, hydrofibres, gauzeetc.

EXAMPLE 5

Incorporation of SSS in a Foam

This example demonstrates how the SSS may be incorporated into a Foamproduct, which is suitable for treating colonised wounds.

EXAMPLE 5A

Incorporation of SSS in a foam during the foaming process.

The SSS produced above was mixed with purified water and PE 6200 to forma homogeneous water phase for the foaming reaction. The water was mixedwith Hypol 2002 and while the mixture still is a fluid, the fluid istransformed into a sheet, and the mixture was allowed to rise into afoam dressing. When the foaming reaction had ended (after app. 15minutes), the foam sheet was dried in an oven at 110° C. for 10 minutes.

In table 4 below, the composition by weight in grams of the differentconstituents is stated.

TABLE 4 Composition of foam products according to the invention whereinSSS is incorporated during foaming. Ingredient Example 6A1 Example 6A2SSS 5 20 Purified water 15 0 PE 6200 0.2 0.2 Hypol 2002 20 20

The resulting antibacterial foams were sterilised at 30 kGy.

EXAMPLE 5B

Incorporation of SSS in foam after the foaming process.

A foam sheet was prepared in a similar as described above, but withoutadding SSS in the process. The amounts of the different ingredient ingrams is stated in the below table 5.

TABLE 5 Composition of a foam produced without adding silver in thefoaming process Ingredients Amount (grams) Purified water 20 PE 6200 0.2Hypol 2002 20

Foam prepared above was immersed in solutions of differentconcentrations of the SSS (prepared by mixing SSS with different amountsof purified water) and allowed to absorb fluid until it was completelysaturated. Then, the fluid was squeezed out of the foam leaving 200%absorbed fluid as compared to the dry weight of the foam. Finally thefoam was dried in an oven at 110° C. to a moisture content below 10% w/w(15 minutes). The composition of the SSS/water mixtures appear from thebelow Table 6.

TABLE 6 SSS/Water mixtures for the incorporation of silver in foamaccording to the invention. Ingredients Example 6B1 Example 6B2 SSS(grams) 10 40 Purified water (grams) 70 40

The final antibacterial foams were sterilised at 30 kGy.

The silver content of each foam sample as determined by AtomicAbsorption appear from the below table 7:

TABLE 7 Sample no. Silver content (mg/g) 6A1 49 6A2 18 6B1 61 6B2 23

EXAMPLE 6

Incorporation of SSS an Amorphous Hydrogel

This example demonstrates how the stabilised silver solution can beincorporated in an amorphous hydrogel for treatment of Wounds. It isalso possible to use other hydrogel formulations in order to obtain anantibacterial amorphous hydrogel.

Preparation of an Amorphous Hydrogel According to the Invention.

A hydrogel was prepared by mixing SSS prepared above, PVP and purifiedwater in a beaker. The composition of the hydrogel prepared is presentedin the below Table 8:

TABLE 8 Composition of the hydrogels according to the invention:Ingredients Sample 7 Purified water 180 grams PVP  12 grams SSS  20grams

After complete solubilisation of the PVP, the solution was transferredinto a syringe and sent to electron beam irradiation (2×20 kGy). Aftersterilisation the gel was squeezed out of the syringe and was in theform of gel particles (an amorphous gel).

EXAMPLE 7

Preparation of Hydrogel Sheets Comprising Diethyl Hydantoin and DimethylBarbiturate

EXAMPLE 7A

Preparation of a Stabilised Silver Solution Comprising DiethylHydantoin.

A stabilised silver solution was prepared as described in example 4, butusing 5,5-diethyl hydantoin instead of dimethyl hydantoin in the samemolar amount. The silver concentration was 0.25% instead of 2% w/w(adjusted with extra purified water giving the same mole ratio betweensilver, diethyl hydantoin and sodium hydroxide as in example 5).

EXAMPLE 7B

Preparation of a Stabilised Silver Solution Comprising DimethylBarbiturate

A stabilised silver solution was prepared as described in example 4, butusing 5,5-dimethyl barbiturate instead of dimethyl hydantoin in the samemolar amount.

The silver concentration was 0.25% instead of 2% w/w. The amount ofsodium hydroxide was adjusted to a level ensuring that the molar ratiobetween sodium hydroxide and silver nitrate was 3.

Hydrogel sheets according to the invention were prepared by mixing thestabilised solution of 5,5-diethyl hydantoin or 5,5-dimethyl barmiturateobtained above, PVP and purified water in a beaker

After complete solubilisation of the PVP in the stabilised silversolution and purified water, the solution was transferred into a sheetshape (5 mm thick) and sent to electron beam irradiation (2×20 kGy).

The compositions of the hydrogel sheets are stated in the below Table 9

TABLE 9 Ingredients Sample 8A Sample 8B Solution of diethyl 160 grams  0grams hydantoin Solution of dimethyl  0 grams 160 grams barbiturate PVP 12 grams  12 grams Purified water  40 grams  40 grams The silvercontent in the Hydrogel sheets were app. 0.2%

EXAMPLE 8

Incorporation of SSS in an Alginate Fabric

A stabilised silver solution was prepared as in example 5, but using63.8 grams of Water, 21.90 grams of 5,5-Di Methyl Hydantoin, 4.80 gramsof Sodium Hydroxide and 9.50 grams of Silver Nitrate.

To this solution was added 50 grams of PEG 600 and 450 grams of 96%ethanol, giving a final silver concentration of 1 w/w %.

Pieces of 100 square cm of an alginate non woven fabric (Algisite M fromS+N) were soaked in the above solution until saturation (about 20 gramssolution per piece) and were squeezed in such a manner that the piecesretained 5 grams of the solution corresponding to 50 mg Silver.

EXAMPLE 9

Antimicrobial Effect

Demonstration of Antimicrobial Effect of Compounds According to theInvention

Isosensitest agar plates were inoculated with Ps. aeruginosa or St.aureus and incubated for 24 hr at 37° C. 10 mm Circles of a sample of acomposition according to the invention were placed on to the agar plates(when testing the amorphous hydrogel, a circular hole of a diameter of10 mm was cut out of the agar plate and filled with the hydrogel). After24 hours, the zone of inhibition was measured and the samples were movedto fresh inoculated and incubated agar plates. The zone of inhibitionwas measured after additional 24 hours (corresponding to a service timeof 48 hours). This was repeated for additional 24 hours (correspondingto a service time of 72 hours).

The results are summarised in the below Table 10 Table 10

TABLE 10 Microbial effect (diameter of zone of inhibition in mm) Ps.Aeruginosa St. Aureus Sample no 24 hours 48 hours 72 hours 24 hours 48hours 72 hours 5A1 10.0 14.3 16.3 10.0 10.0 10.0 5A2 14.0 20.0 17.7 13.014.0 10.3 5B1 11.0 10.0 10.0 10.0 0.0 0.0 5B2 16.0 19.0 16.7 16.0 16.314.0 6    21.0 45.7 23.3 21.3 15.0 14.3 7A  16.0 20.0 24.0 14.5 14.514.5 7B  14.0 19.5 23.0 16.0 14.0 14.0 8    16.0 12.0 10.0 18.0 13.012.0

The results show that wound care products comprising silver complexes ofthe invention show an antibacterial activity for more than 72 hours.

From Examples 5A and 5B it appears that the total load of silverinfluences the antimicrobial properties.

The invention claimed is:
 1. A stabilized composition havingantibacterial, antiviral and/or antifungal activity, said compositioncontaining silver ions in complex with a ligand, wherein saidcomposition comprising a complex of silver ions; and a ligand selectedfrom the group consisting of: 5,5-dimethyl-barbituric acid or1,5,5-trimethyl-barbituric acid, wherein said silver ions are stabilizedagainst reduction to free silver in a hydrophilic environment and thecomposition has a solubility in water greater than 10 mg Ag/l.
 2. Acomposition as claimed in claim 1, wherein said composition contains asecond silver compound with a solubility less than 10 mg Ag/l.
 3. Acomposition as claimed in claim 1, wherein said composition is mixedinto a polymer composition.
 4. A composition according to claim 3,wherein the polymer is a hydrophilic polymer.
 5. A composition asclaimed in claim 4, wherein the hydrophilic polymer forms a gel, a foamor a xerogel.
 6. A composition as claimed in claim 4, wherein saidcomposition is mixed into an alginate.
 7. A composition as claimed inclaim 1, wherein the concentration of silver is from 0.1 to 20% byweight of the dry matter.
 8. A method of producing the composition ofclaim 1, said method comprising the steps of: 1) dissolving a silversalt in water; 2) adding a ligand selected from the group consisting of5,5-dimethyl-barbituric acid or 1,5,5-trimethyl-barbituric acid to thesolution of the silver salt at a controlled pH; 3) leaving the resultingsolution for a period of between about 2 to 100 hours; 4) optionallyadjusting the pH to a value of 7-11; 5) isolating the resulting mixture;and 6) optionally drying and micronizing the mixture.
 9. A medicaldevice which comprises the the composition of claim
 1. 10. A method oftreating infection in a human being by applying the medical device ofclaim
 9. 11. The medical device of claim 9, wherein said device is acatheter having a hydrophilic coating.
 12. The method of treatinginfection in a human being of claim 10, wherein said medical device is acatheter having a hydrophilic coating.
 13. The medical device accordingto claim 9, wherein the medical devices is selected from the groupconsisting of a wound dressing, an ostomy appliance, and an incontinencedevice.